[Elecraft] Re: K2 mods

[Wayne Burdick]

Pete,

You asked about the 0.1-volt drop diode I mentioned in the updated K2 announcement. This
is a special type of diode that is optimized for low voltage "battery-ORing" and
reverse-polarity-protection applications. In exchange for that extremely low forward
voltage drop, you have to accept a larger reverse leakage current, on the order of 1-10
mA, varying with temperature and reverse voltage. But this current--which would flow if
you really did connect the power supply backwards--is still small enough that it can't
damage the rig with polarity reversed. So it's a good device to use here. 

The specific part we're using is an International Rectifier 95SQ015. It's rated at 9 amps
peak pulse power, and can easily handle the current needed by the K2 at maximum power
output. As with other diodes, the forward drop increases with forward current. At typical
transmit levels, the drop is 0.2 to 0.25 V, which is still very small compared with
ordinary power shottky diodes. 

The reason we added this high-performance diode is to provide additional margin for
low-voltage operation, such as from 9.6 V battery packs, as well as to save a bit of power
that would ordinarily be dissipated by the diode on transmit. Also, we use the same diode
in our K1 and K2 internal battery options, and wanted to standardize.

73,
Wayne
N6KR


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